Towing stability is directly related to the distance between the rear axle and tow-ball, the shorter the distance the greater the towing stability, the longer the distance the less the stability.
4×4 pickups are heavy with nice torquey engines which is a good, sure footed place from which to start, however they nearly all have long rear overhangs with the tow-ball mounted a long way aft of the axle. When towing heavy trailers you are constantly reminded of this.
Mounting a small demountable with correct forward weight bias will generally improve stability, however you should think seriously about the wisdom of towing if your rear axle is approaching it’s maximum loading, especially if weight has been transferred aft from the front axle as tends to be the case with poorly designed and overweight demountables.
Tow Bar extensions. You should not consider extending the tow bar under any circumstances. We are aware that such extensions are available and whilst they may be mechanically ‘safe’ (in that they may not physically break) stability will be significantly and worryingly decreased. You cannot cheat physics.
Towing is still possible even with a long overhang, with the right trailer. Examples of this can be seen with any HGV rigid/drawbar trailer combination. This a typical example, the extended draw bar and very short axle to ball-hitch distance offers superb stability and great manoeuvrability.